#include<stdio.h>
int main() 
{
	int a,b,c,n,i;
	scanf("%d",&n);
	for (i=1;i<=n;i++)
		if (i<=2)  a=b=c=1;
		else {
			 	c=a+b;  
			 	a=b;
			 	b=c;
		     }
	printf("%d",2*c);	     
	return 0;	
}
